The previous test results will also be used in grading and staging the
cancer. The grade refers to how aggressive (likely to spread quickly)
the cancer appears. Staging refers to the size of the cancerous area and
whether or not it has spread out. Grading and staging help the doctors to
choose the treatment most appropriate to each individual.
According to the American Cancer Society, the most common system used for
staging most, but not all, bone cancer is the TNM system of the American
Joint Committee on Cancer.
T stands for tumor, regardless of where it is located on the bone.
N signifies that it has spread to lymph nodes (pockets immune system
cells found throughout the body.
M means that it has metastasized.
T1—The tumor is no bigger
than 8cm.
T2— The tumor is larger than
8 cm.
T3—The tumor has skipped to
other areas in the bone.
T4—The tumor has directly
invaded a surrounding organ.
N0—The lymph nodes show no
sign of cancerous cells.
N1—Lymph nodes have cancer
cells in them (Very rare with bone cancer)
M0—No bone cancer has spread
to other parts of the body.
M1a—The cancer has spread to
the lung.
M2b—The cancer has spread to
sites other than the lung.
An additional factor called the histological grade is used in staging bone
cancer. While there technically 4 grades, it is common in the medical field for
doctors to refer to just 2—high grade and low grade.
G1—low grade, well
differentiated (cells appear the least aggressive)
G2—low grade, moderately
differentiated (intermediate between G1 and G3)
G3—high grade, poorly
differentiated (cells appear more aggressive)
G4—high grade, not
differentiated (cells appear extremely aggressive)
A stage is assigned based on the all the information about the tumor and its
behavior. This process is called stage grouping and the stages are as
follow:
Stage IA (G1, 2; T1;
N0; M0): The cancer is low grade, smaller than 8 cm, and has not spread.
Stage IB (G1, 2; T2;
N0; M0): The cancer is low grade, larger than 8 cm, and has not spread.
Stage IIA (G3, 4; T1;
N0; M0): This high grade cancer is smaller than 8 cm and has not spread.
Stage IIB (G3, 4; T2;
N0, M0): This high grade cancer is larger than 8 cm and has not spread.
Stage III (Any G, T3;
N0; M0): This any-grade tumor has spread within the bone, but not out.
Stage IVA (Any G, Any
T; N0; M1a): The cancer has spread to only the lungs.
Stage IVB (Any G; Any
T; N1; Any M) or (Any G; Any T; Any N; M1b): The cancer has spread to
lymph nodes and/or sites other than the lungs.
Bone cancer that returns after an initial treatment is called recurrent
bone cancer.